Managing Doppler and Framing Impacts in Networks

ABSTRACT

A method includes receiving a current velocity and a current position of a mobile node relative to a fixed node. The method also includes identifying a receive time slot for the fixed node to receive a transmission of a data packet from the mobile node and determining a propagation delay for the data packet between the mobile node and the fixed node based on the current position of the mobile node. The method includes determining a transmission time based on the receive time slot and the propagation delay and determining a Doppler shift based on the current velocity of the mobile node. The method includes determining a transmission frequency based on the Doppler shift and a clock rate correction. The method also includes transmitting the data packet to the fixed node at the determined transmission time using the determined transmission frequency compensated by the determined clock rate correction.

TECHNICAL FIELD

This disclosure relates to managing Doppler and framing impacts innetworks.

BACKGROUND

Communications between nodes with high relative velocity cause signalsto be received at different frequencies than transmitted, and changes inreceiver to transmitter distances within one timing cycle will changethe perceived clock rate at the receiver. There are many waveformdesigns that include features that address Doppler and other velocityrelated issues. For any given pilot symbol population, there is aspecific limit to the Doppler that can be addressed and the link willfail beyond that limit.

SUMMARY

One aspect of the disclosure provides receiving, at data processinghardware of a mobile node, a current velocity of the mobile node and acurrent position of the mobile node relative to a fixed node. The mobilenode is moving toward or away from the fixed node. The method alsoincludes identifying, by the data processing hardware, a receive timeslot for the fixed node to receive a transmission of a data packet fromthe mobile node and determining, by the data processing hardware, apropagation delay for the data packet between the mobile node and thefixed node based on the current position of the mobile node relative tothe fixed node. The method also includes determining, by the dataprocessing hardware, a transmission time based on the identified receivetime slot and the determined propagation delay and determining, by thedata processing hardware, a Doppler shift based on the current velocityof the mobile node. The method also includes determining, by the dataprocessing hardware, a transmission frequency based on the determinedDoppler shift and determining, by the data processing hardware, a clockrate correction. The clock rate correction accounts for a change in thepropagation delay during transmission of the data packet. The methodalso includes transmitting, by the data processing hardware, the datapacket to the fixed node at the determined transmission time using thedetermined transmission frequency compensated by the determined clockrate correction.

Implementations of the disclosure may include one or more of thefollowing optional features. In some implementations, determining thetransmission time includes subtracting the propagation delay from theidentified receive time slot. In some examples, determining thetransmission frequency includes adding the Doppler shift to a basetransmission frequency or subtracting the Doppler shift from the basetransmission frequency. Determining the clock rate correction mayinclude estimating an end position of the mobile node. The end positionis a position of the mobile node relative to the fixed node at the endof transmitting the data packet. Determining the clock rate correctionmay also include determining a difference between the current positionof the mobile node and the end position of the mobile node anddetermining the clock rate correction based on the determined differencebetween the current position of the mobile node and the end position ofthe mobile node. Determining the clock rate correction, in someimplementations, further includes adjusting a symbol rate of the datapacket based on the determined difference between the current positionof the mobile node and the end position of the mobile node. The adjustedsymbol rate may be equivalent to a symbol count of an uncorrectedwaveform.

Another aspect of the disclosure provides receiving, at data processinghardware of a fixed node, a current velocity of a mobile node and acurrent position of the mobile node relative to the fixed node. Themobile node is moving toward or away from the fixed node. The methodalso includes identifying, by the data processing hardware, a receivetime slot for the fixed node to receive a transmission of a data packetfrom the mobile node and determining, by the data processing hardware, apropagation delay for the data packet between the mobile node and thefixed node based on the current position of the mobile node relative tothe fixed node. The method also includes determining, by the dataprocessing hardware, a reception time based on the identified receivetime slot and the determined propagation delay and determining, by thedata processing hardware, a Doppler shift based on the current velocityof the mobile node. The method also includes determining, by the dataprocessing hardware, a reception frequency based on the determinedDoppler shift and determining, by the data processing hardware, a clockrate correction. The clock rate correction accounts for a change in thepropagation delay during transmission of the data packet. The methodalso includes transmitting, by the data processing hardware, the datapacket to the mobile node at the determined reception time using thedetermined reception frequency compensated by the determined clock ratecorrection.

This aspect may include one or more of the following optional features.In some implementations, determining the reception time includessubtracting the propagation delay from the identified receive time slot.In some examples, determining the reception frequency includes addingthe Doppler shift to a base reception frequency or subtracting theDoppler shift from the base reception frequency. Determining the clockrate correction may include estimating an end position of the mobilenode. The end position is a position of the mobile node relative to thefixed node at the end of transmitting the data packet. Determining theclock rate correction may also include determining a difference betweenthe current position of the mobile node and the end position of themobile node and determining the clock rate correction based on thedetermined difference between the current position of the mobile nodeand the end position of the mobile node. Determining the clock ratecorrection, in some implementations, further includes adjusting a symbolrate of the data packet based on the determined difference between thecurrent position of the mobile node and the end position of the mobilenode. The adjusted symbol rate may be equivalent to a symbol count of anuncorrected waveform.

Another aspect of the disclosure provides a system that includes dataprocessing hardware of a mobile node and memory hardware incommunication with the data processing hardware. The memory hardwarestores instructions that when executed on the data processing hardwarecause the data processing hardware to perform operations that includereceiving a current velocity of the mobile node and a current positionof the mobile node relative to a fixed node. The mobile node is movingtoward or away from the fixed node. The method also includes identifyinga receive time slot for the fixed node to receive a transmission of adata packet from the mobile node and determining a propagation delay forthe data packet between the mobile node and the fixed node based on thecurrent position of the mobile node relative to the fixed node. Themethod also includes determining a transmission time based on theidentified receive time slot and the determined propagation delay anddetermining a Doppler shift based on the current velocity of the mobilenode. The method also includes determining a transmission frequencybased on the determined Doppler shift and determining a clock ratecorrection. The clock rate correction accounts for a change in thepropagation delay during transmission of the data packet. The methodalso includes transmitting the data packet to the fixed node at thedetermined transmission time using the determined transmission frequencycompensated by the determined clock rate correction.

This aspect may include one or more of the following optional features.In some implementations, determining the transmission time includessubtracting the propagation delay from the identified receive time slot.In some examples, determining the transmission frequency includes addingthe Doppler shift to a base transmission frequency or subtracting theDoppler shift from the base transmission frequency. Determining theclock rate correction may include estimating an end position of themobile node. The end position is a position of the mobile node relativeto the fixed node at the end of transmitting the data packet.Determining the clock rate correction may also include determining adifference between the current position of the mobile node and the endposition of the mobile node and determining the clock rate correctionbased on the determined difference between the current position of themobile node and the end position of the mobile node. Determining theclock rate correction, in some implementations, further includesadjusting a symbol rate of the data packet based on the determineddifference between the current position of the mobile node and the endposition of the mobile node. The adjusted symbol rate may be equivalentto a symbol count of an uncorrected waveform.

Another aspect of the disclosure provides a system that includes dataprocessing hardware of a fixed node and memory hardware in communicationwith the data processing hardware. The memory hardware storesinstructions that when executed on the data processing hardware causethe data processing hardware to perform operations that includereceiving a current velocity of the mobile node and a current positionof the mobile node relative to a fixed node. The mobile node is movingtoward or away from the fixed node. The method also includes identifyinga receive time slot for the fixed node to receive a transmission of adata packet from the mobile node and determining a propagation delay forthe data packet between the mobile node and the fixed node based on thecurrent position of the mobile node relative to the fixed node. Themethod also includes determining a reception time based on theidentified receive time slot and the determined propagation delay anddetermining a Doppler shift based on the current velocity of the mobilenode. The method also includes determining a reception frequency basedon the determined Doppler shift and determining a clock rate correction.The clock rate correction accounts for a change in the propagation delayduring transmission of the data packet. The method also includestransmitting the data packet to the mobile node at the determinedreception time using the determined reception frequency compensated bythe determined clock rate correction.

This aspect may include one or more of the following optional features.In some implementations, determining the reception time includessubtracting the propagation delay from the identified receive time slot.In some examples, determining the reception frequency includes addingthe Doppler shift to a base reception frequency or subtracting theDoppler shift from the base reception frequency. Determining the clockrate correction may include estimating an end position of the mobilenode. The end position is a position of the mobile node relative to thefixed node at the end of transmitting the data packet. Determining theclock rate correction may also include determining a difference betweenthe current position of the mobile node and the end position of themobile node and determining the clock rate correction based on thedetermined difference between the current position of the mobile nodeand the end position of the mobile node. Determining the clock ratecorrection, in some implementations, further includes adjusting a symbolrate of the data packet based on the determined difference between thecurrent position of the mobile node and the end position of the mobilenode. The adjusted symbol rate may be equivalent to a symbol count of anuncorrected waveform.

The details of one or more implementations of the disclosure are setforth in the accompanying drawings and the description below. Otheraspects, features, and advantages will be apparent from the descriptionand drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of an exemplary communication system.

FIG. 2 is a schematic view of an exemplary communication system thatincludes a mobile node and a fixed node.

FIG. 3A is a schematic view of an exemplary communication array of amobile node.

FIG. 3B is a schematic view of an exemplary communication array of afixed node.

FIG. 4 is a flowchart of an example method for managing Doppler andframing impacts in networks.

FIG. 5 is a flowchart for another example method for managing Dopplerand framing impacts in networks.

FIG. 6 is a schematic view of an example computing device that may beused to implement the systems and methods described herein.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Communications between two or more nodes with high relative velocitycause signals communicated between the nodes to be received by thereceiver node at a frequency different from the transmission frequencyand changes in distance between the transmitter node and the receivernode within one timing cycle also changes the perceived clock rate atthe receiver node. Additionally, the distance between the two nodescauses transmissions to collide at the receiver node in atime-synchronized network. These effects cause both failure of theintended communications and interference with other communications.Traditionally, these issues in communications networks with moving nodesare addressed by providing extensive additional timing information inthe signal to enable the receiver node to track and compensate for theseeffects. For instance, these traditional solutions include embeddingpilot symbols throughout the transmitted block in order to provide thereceiver the information required to track Doppler shift and timingchanges. However, this compensation adds overhead to the signal, whichreduces the throughput, complicates receiver design, and increasesprocessing overhead. Further, this approach still fails to directlycompensate for collisions in time synchronized networks. Instead,collisions are addressed by expanding guard times to accommodate worstcase ranges of propagation delay due to the speed of light. Somewaveforms and access methods define a maximum velocity difference andpropagation delay for which the waveform or method is designed. Forexample, a waveform may have pilot symbols embedded throughout atransmitted block in order to provide the receiver the informationrequired to track Doppler shift and timing changes. Expanding theselimits may be possible, but such expansion further reduces theeffectiveness of the system, while simultaneously adding additionalcomplexity. Thus, many communications systems are designed for a verylimited range of operation, and fail to operate once outside of theselimits. These communication systems are inflexible and any extensionrequires significant engineering. For example, the Long-Term Evolution(LTE) standard required a unique version to be designed whentransitioning from automobiles to high-speed trains in order to increasethe Doppler range, as the speed increase from automobiles to trainsrendered the version ineffective.

Referring to FIG. 1, in some implementations, a global-scalecommunication system 100 includes gateways or fixed nodes 110 (e.g.,source ground stations 110 a and destination ground stations 110 b) andmobile nodes 120 (e.g., aircraft 120 a, high altitude platforms (HAPs)120 b, and satellites 120 c). The fixed nodes 110 communicate with themobile nodes 120 (i.e., transmit and receive data packets or data blocks10) while the mobile nodes 120 are moving (either toward or away fromthe fixed node 110). The mobile nodes 120 may have a high relativevelocity with respect to the fixed nodes 110. In some examples, thesource ground stations 110 a may communicate with the satellites 120 c,the satellites 120 c may communicate with the HAPs 120 b, and the HAPs120 b may communicate with the destination ground stations 110 b. Insome examples, the source ground stations 110 a also operate aslinking-gateways between satellites 120 c. The source ground stations110 a may be connected to one or more service providers and thedestination ground stations 110 b may be user terminals (e.g., mobiledevices, residential WiFi devices, home networks, etc.). In someimplementations, a HAP 120 b is an aerial communication device thatoperates at high altitudes (e.g., 17-22 km). The HAP 120 b may bereleased into the earth's atmosphere, e.g., by an air craft, or flown tothe desired height. Moreover, the HAP 120 b may operate as aquasi-stationary aircraft. In some examples, the HAP 120 b is anaircraft 120 a, such as an unmanned aerial vehicle (UAV); while in otherexamples, the HAP 120 b is a communication balloon 120 b. The satellite120 c may be in Low Earth Orbit (LEO), Medium Earth Orbit (MEO), or HighEarth Orbit (HEO), including Geosynchronous Earth Orbit (GEO).

The HAPs 120 b and satellites 120 c may move about the earth 5 along apath, trajectory, or orbit (also referred to as a plane, since theirorbit or trajectory may approximately form a geometric plane). Moreover,several HAPs 120 b or satellites 120 c may operate in the same ordifferent orbits. Multiple satellites 120 c working in concert form asatellite constellation. The satellites 120 c within the satelliteconstellation may operate in a coordinated fashion to overlap in groundcoverage.

FIG. 2 provides a schematic view of an exemplary architecture of acommunication system 200 establishing a communications link between amobile node 120 and a fixed node 110 (e.g., a ground terminal 110). Inthe example shown, the mobile node 120 includes a body 210 that supportsa communication array 300, 300 a, which can communicate with the groundstation 110 through a communication 20 (e.g., radio signals orelectromagnetic energy) using antennas 310. The ground station 110includes an antenna 310 designed to communicate with the mobile node 120and may also include a communication array 300 b (that includes antenna310). That is, either or both the mobile node 120 and the fixed node 110may include the communication array 300. The communication array 300includes data processing hardware 312 for processing the receiving andtransmitting of data 10 via communications 20. The mobile node 120 maycommunicate various data and information to the fixed node 110, such as,but not limited to, airspeed, heading, attitude position, temperature,GPS (global positioning system) coordinates, wind conditions, flightplan information, fuel quantity, battery quantity, data received fromother sources, data received from other antennas, sensor data, etc. Asused herein, the terms “data 10”, “data packets 10”, and block are usedinterchangeably. The ground station 110 may communicate to the mobilenode 120 various data and information, such as, but not limited to,flight directions, flight condition warnings, control inputs, requestsfor information, requests for sensor data, data to be retransmitted viaother antennas or systems, etc. The mobile node 120 may be variousimplementations of flying craft including, but not limited to, anairplane, airship, helicopter, gyrocopter, blimp, multi-copter, glider,balloon, fixed wing, rotary wing, rotor aircraft, lifting body, heavierthan air craft, lighter than air craft, etc.

The fixed node 110 and the mobile node 120 may communicate with anyappropriate communication method. For example, the nodes 110, 120 maycommunicate using time-division multiplexing (TDM). In TDM, the timedomain is divided into several recurrent time slots of typically fixedlength, one time slot for each sub-channel of the communication channel.Thus, one node (e.g., a fixed node 110) may communicate with many othernodes (e.g., mobile nodes 120) simultaneously over the samecommunication channel while efficiently using the available bandwidth.Such systems generally agree on a fixed block size (i.e., the size ofeach data transmission) and a fixed frequency (i.e., a base frequency).

One of the challenges associated with establishing a communicationsystem between a mobile node 120 and fixed node 110 is the movement anddistance of the mobile node 120 relative to the fixed node 110.Implementations of the present disclosure present a communication arraywith a combination of systems to allow for managing Doppler and framingimpacts in a high speed, many to one or one to many network betweenmobile nodes 120 and fixed nodes 110. FIGS. 3A and 3B provide schematicviews of exemplary architectures of the communication array 300 of amobile node 120 (FIG. 3A) and a fixed node 110 (FIG. 3B). Thecommunication array 300 includes antennas 310 that transmit/receive datapackets 10 by emitting/receiving a series of electromagnetic signals320. An electromagnetic signal 320 may include a corresponding signalfrequency, representing a rate at which a base signal or carrier waveassociated with the electromagnetic signal 320 occurs over a period oftime, and a corresponding signal transmission period, representing atime at which the antennas 310 are transmitting the data packets 10. Thesignal frequency may also be representative of a channel used by theelectromagnetic signal 320 within a given frequency band.

With continued reference to FIGS. 3A and 3B, a signal controller 330controls the antennas 310 to emit electromagnetic signals 320 whentransmitting data packets 10 and to receive electromagnetic signals 320when receiving data packets 10. In the example shown, the signalcontroller 330 includes a time slot controller 332, a frequencycontroller 334, and a correction controller 336. The signal controller330 receives (e.g., from another system or module of the same system) acurrent velocity 340 of the mobile node 120 and a current position 342of the mobile node 120 relative to the fixed node 110. As used herein,the current position 342 may refer to a distance between the mobile node120 and the fixed node 110. Moreover, while the term “mobile” impliesthe mobile node 120 is moving, the fixed node may be stationary (i.e.,not moving) or may also be moving. Accordingly, when the signalcontroller 330 is located at the mobile node 120 (FIG. 3A), the signalcontroller 330 receives corresponding information related to thevelocity 340 of the mobile node 120 and the position 342 of the mobilenode 120 relative to the fixed node 110 prior to communicating with thefixed node 110. Similarly, when the signal controller 330 is located atthe fixed node 110 (FIG. 3B), the signal controller 330 receivesinformation about the velocity 340 of the mobile node 120 and theposition 342 of the mobile node 120 (again, relative to the fixed node110) prior to communicating with the mobile node 120.

When the signal controller 330 is scheduling transmission of data 10,the time slot controller 332 identifies or controls selection of areceive time slot (t_(slot)) that indicates an intended time for thetransmission of the data 10 to be received by the receiving node 110,120. The time slot controller 332 also determines a propagation delay(t_(delay)) for the transmission of the data 10 between the transmittingnode (e.g., one of the fixed node 110 or the mobile node 120) and thereceiving node (e.g., the other one of the fixed node 110 or the mobilenode 120) based on the current position 342 of the mobile node 120relative to the fixed node 110. For instance, in the example of FIG. 3Awhen the signal controller 330 at the mobile node 120 is schedulingtransmission of data 10 (e.g., by emitting a corresponding series of oneor more electromagnetic signals 320), the time slot controller 332identifies the receive time slot (t_(slot)) indicating the intended timefor the transmission of the data 10 from mobile node 120 to be receivedby the fixed node 110. On the other hand, in the example of FIG. 3B, thetime slot controller 332 at the fixed node 110 identifies the receivetime slot indicating the intended time for the transmission of data 10from the fixed node 110 to be received by the mobile node 120.Accordingly, the time slot controller 332 determines the propagationdelay (due to the speed of light c and the distance d) between the nodes110, 120. For example, the propagation delay may be calculated asfollows:

$\begin{matrix}{t_{delay} = \frac{d}{c}} & (1)\end{matrix}$

As illustrated in FIG. 3A, the time slot controller 332 of the mobilenode 120 may then determine a transmission time 350 (t_(xmit)) based onthe intended receive time slot and the propagation delay. The time slotcontroller 332 may offset the transmission time 350 from the intendedtime slot by the propagation delay. That is, the mobile node 120 maytransmit earlier than originally intended by a quantity equivalent tothe propagation delay. Specifically, when the mobile node 120 istransmitting, the transmission time 350 may be calculated as follows:

t _(xmit) =t _(slot) −t _(delay)  (2)

As illustrated in FIG. 3B, the time slot controller 332 of the fixednode 110 may instead determine a reception time 360 (as opposed to thetransmission time 350 of the mobile node 120 (FIG. 3A)) when the fixednode 110 is transmitting data 10 to the mobile node 120. The receptiontime 360 is the time slot that the mobile node 120 will receive thetransmission from the fixed node 110. The reception time 160, in someexamples, is set to a quantity of time equivalent to the propagationdelay after the scheduled transmit time of the fixed node 110 (i.e.,when the time slot the mobile node 120 will actually receive thetransmission when the fixed node 110 transmits at its scheduled transmittime). Specifically, when the fixed node 110 is transmitting, thereception time 360 may be calculated as follows:

t _(receive) =t _(slot) +t _(delay)  (3)

The frequency controller 334 controls the transmission frequency of thedata 10. Because of the relative velocity difference between the nodes110, 120, the mobile node 120 will receive the data transmission at adifferent frequency than a frequency at which the data 10 wastransmitted (i.e., a Doppler shift). To account for this change infrequency, the frequency controller 334 determines a Doppler shift(f_(shift)) for the transmission of the data 10 based on the currentvelocity 340 of the mobile node 120. Since the fixed node 110 could bestationary or moving, the current velocity 340 of the mobile node 120relative to the fixed node 110 corresponds to a velocity difference(v_(diff)). Thus, the velocity difference could be the actual velocityof the mobile node 120 when the fixed node 110 is stationary, or whenthe fixed node 110 is also moving, the velocity difference is simply thedifference in velocity between the mobile and fixed nodes 110, 120. Forexample, the Doppler shift may be calculated as follows:

$\begin{matrix}{f_{shift} = \frac{v_{diff}}{c}} & (4)\end{matrix}$

The polarity of equation (3) indicates whether the mobile node 120 ismoving toward or away from the fixed node 110. Referring back to FIG.3A, when the mobile node 120 is transmitting, a transmission frequency352 (f_(xmit)) is calculated using a base transmission frequencyf_(fixed) and the Doppler shift f_(shift) as follows:

f _(xmit) =f _(fixed) +f _(shift)  (5)

The base frequency represents the original intended frequency of thedata transmission while the Doppler shift represents a compensation ofthe frequency change due to Doppler shift. The combination of the basefrequency and the Doppler shift results in the transmission frequency352 by which the mobile node 120 will transmit the data 10. Referringnow again to FIG. 3B, when the fixed node 110 is transmitting, areception frequency 362 (f_(receive)) is calculated also using the basetransmission frequency and the Doppler shift. The reception frequency,which represents the frequency by which the mobile node 120 will receivethe data 10, may be calculated as follows:

f _(receive) =f _(fixed) +f _(shift)  (6)

During data transmission of the data packet 10, the mobile node 120 willcontinue to move away from or toward the fixed node 110. Therefore, themobile node 120 will have a distance from the fixed node 110 at thebeginning of the data transmission (the current position 342) that isdifferent than a distance from the fixed node 110 at the end of the datatransmission (an end position). Thus, the propagation delay changesthroughout transmission of the data packet 10. The correction controller336 compensates for this effect by accounting for the change in thepropagation delay during transmission of the data packet 10. In someexamples, the correction controller 336 estimates an end position of themobile node 120. The end position is a position of the mobile node 120relative to the fixed node 110 at the end of the transmission of thedata packet 10 (i.e., the estimated future position of the mobile node120 at the end of data transmission). For instance, when the mobile node120 is the transmitting node and the fixed node 110 is the receivingnode, the end position of the mobile node 120 corresponds to theestimated future position of the mobile node 120 at the timetransmission of the data packet 10 from the mobile node 120 is receivedby the fixed node 110. The correction controller 336 then determines adifference r_(change) between the current position 342 (i.e., theposition at the beginning of the data transmission) and the endposition. This difference r_(change) introduces a framing error into thedata transmission (i.e., how much data is received by the receivernode). In some implementations, compensation t_(comp) for this framingerror is calculated as follows:

$\begin{matrix}{t_{comp} = \frac{r_{change}}{c}} & (7)\end{matrix}$

A clock rate correction t_(comp) 354 may adjust a symbol rate of thedata packet 10 in order to lengthen or shorten the transmission orreception of the data packet 10. That is, if the nodes 110, 120 aremoving apart (i.e., r_(change) is positive) and the mobile node 110 istransmitting (FIG. 3A), the clock rate correction 354 shortens the blocktransmission (i.e., the symbol rate is reduced). Alternatively, if thenodes 110, 120 are moving apart and the fixed node 110 is transmitting(FIG. 3B), the block reception is lengthened (i.e., the symbol rate isincreased). On the other hand, if the nodes 110, 120 are moving closertogether (i.e., r_(change) is negative) and the mobile node 120 istransmitting (FIG. 3A), the clock rate correction 354 lengthens theblock transmission. Likewise, if the fixed node 110 is transmitting(FIG. 3B) and the nodes 110, 120 are moving closer together, the blockreception is shortened. Because the fixed node 110 and the mobile node120 typically agree on a fixed block size, the symbol rate may beadjusted or compensated to have a symbol account equivalent to anuncorrected waveform. That is, the clock rate correction 354 may adjustthe symbol rate such that the receiving node (mobile node 120 or fixednode 110) perceives the same symbol rate as the node would perceive ifthe position between the fixed node 110 and the mobile node 120 werefixed (i.e., the mobile node 120 was not moving).

If the mobile node 120 is accelerating such that the difference inDoppler shift and timing correction is beyond the tolerance of thereceiving node (mobile node 120 or fixed node 110), the clock ratecorrection 354 may be performed multiple times within a single datapacket 10 to correct each segment of the data packet 10 in order toensure that the entire packet 10 is received within the processinglimits. In some implementations, physical limitations of mobility of themobile node 120 in relationship to block size may preclude clock ratecorrection, which may be determined in advance (through, for example,the same or similar process).

The fixed nodes 110 and mobile nodes 120 of FIG. 1-3B are exemplaryonly. The communication array 300 is suitable for communication betweenone or more fixed and mobile nodes 110, 120, including a mobile node 120to a fixed node 110, a fixed node 110 to a mobile node 120, and a mobilenode 120 to another mobile node 120. The node 110, 120 may be a networknode (of which there may be many) or the node 110, 120 may be a centralnode (of which there may be one in communication with many networknodes). In order to minimize interference, transmissions may be designedto only be received by a single fixed node 110 (or central node) at atime (i.e., using highly directional antennas or only a single fixednode 110). This assures that transmissions do not interfere with anyother synchronized fixed nodes 110. The present disclosure is especiallyeffective with applications that are integrated into platforms that arevery “self aware”. For example, applications with highly reliable, andrapidly updated, position and state vector data, such as through with aninertial measurement unit (IMU) or high performance global positionsystem (GPS). The communication array 300 simplifies the implementationof networks and avoids adding waveform overhead to address worst caseconditions, and thus, enables effectively unlimited network velocitiesand accelerations. Specific tailoring may be applied in any one specificapplication depending upon the dynamics of the platforms involved. Forexample, when the acceleration between the nodes 110, 120 is low, nointra-block corrections may be required.

FIG. 4 is a flowchart of an example method 400 for managing Doppler andframing impacts in networks. The flowchart starts at operation 402 byreceiving, at data processing hardware 312 of a mobile node 120, acurrent velocity 340 of the mobile node 120 and a current position 342of a mobile node 120 relative to a fixed node 110. The mobile node 120is moving toward or away from the fixed node 110. The method 400, atoperation 404, includes identifying, by the data processing hardware312, a receive time slot for the fixed node 110 to receive atransmission of a data packet 10 from the mobile node 120.

At operation 406, the method 400 includes determining, by the dataprocessing hardware 312, a propagation delay for the data packet 10between the mobile node 120 and the fixed node 110 based on the position342 of the mobile node 120 relative to the fixed node 110 (e.g., thetime slot controller 332 using Equation (1)).

The method 400, at operation 408, includes determining, by the dataprocessing hardware 312, a transmission time 350 based on the identifiedreceive time slot and the determined propagation delay. In someexamples, determining the transmission time 350 includes the time slotcontroller 332 using Equation (2) to subtract the propagation delay fromthe identified receive time slot. At operation 410, the method 400includes determining, by the data processing hardware 312, a Dopplershift based on the current velocity 340 of the mobile node 120 (e.g.,the frequency controller 334 using Equation (4)). The method 400, atoperation 412, includes determining, by the data processing hardware312, a transmission frequency 352 based on the determined Doppler shift.In some implementations, determining the transmission frequency 352includes adding, by the frequency controller 334 using Equation (5), aDoppler shift to a base transmission frequency or subtracting theDoppler shift from the base transmission frequency.

The method 400, at operation 414, includes determining, by the dataprocessing hardware 312, a clock rate correction 354. The clock ratecorrection 354 accounts for a change in the propagation delay duringtransmission of the data packet 10. In some examples, determining theclock rate correction 354 includes estimating, by the correctioncontroller 336, an end position of the mobile node 120, the end positioncorresponding to a position of the mobile node 120 relative to the fixednode 110 at the end of transmitting the data packet 10. Determining theclock rate correction 354 may also include determining a differencebetween the current position 342 of the mobile node 120 and the endposition of the mobile node 120 and determining the clock ratecorrection 354 based on the determined difference between the currentposition 342 of the mobile node 120 and the end position of the mobilenode 120 (e.g., Equation (7)). In some implementations, determining theclock rate correction 354 further includes adjusting a symbol rate ofthe data packet 10 based on the determined difference between thecurrent position 342 of the mobile node 120 and the end position of themobile node 120. The adjusted symbol rate may be equivalent to a symbolcount of an uncorrected waveform.

At operation 416, the method 400 includes transmitting, by the dataprocessing hardware 312, the data packet 10 to a fixed node 110 at thedetermined transmission time 350 using the determined transmissionfrequency 352 compensated by the determined clock rate correction 354.

FIG. 5 is a flowchart of another example method 500 for managing Dopplerand framing impacts in networks. The flowchart starts at operation 502by receiving, at data processing hardware 312 of a fixed node 110, acurrent velocity 340 of a mobile node 120 and a current position 342 ofthe mobile node 120 relative to the fixed node 110. The mobile node 120is moving toward or away from the fixed node 110. The method 500, atoperation 504, includes identifying, by the data processing hardware312, a receive time slot for the mobile node 120 to receive atransmission of a data packet 10 from the fixed node 110.

At operation 506, the method 500 includes determining, by the dataprocessing hardware 312, a propagation delay for the data packet 10between the mobile node 120 and the fixed node 110 based on the position342 of the mobile node 120 relative to the fixed node 110. In someimplementations, the time slot controller 332 determines the propagationdelay using Equation (1).

The method 500, at operation 508, includes determining, by the dataprocessing hardware 312, a reception time 360 based on the identifiedreceive time slot and the determined propagation delay. In someexamples, determining the reception time 360 includes the time slotcontroller 332 using Equation (3) to add the propagation delay to theidentified receive time slot. At operation 510, the method 500 includesdetermining, by the data processing hardware 312, a Doppler shift basedon the current velocity 340 of the mobile node 120. For example, thefrequency controller 334 may determine the Doppler shift using Equation(4). The method 500, at operation 512, includes determining, by the dataprocessing hardware 312, a reception frequency 362 based on thedetermined Doppler shift. In some implementations, determining thereception frequency 362 includes adding a Doppler shift to a basereception frequency or subtracting the Doppler shift from the basereception frequency (e.g., Equation (6)).

The method 500, at operation 514, includes determining, by the dataprocessing hardware 312, a clock rate correction 354. The clock ratecorrection 354 accounts for a change in the propagation delay duringtransmission of the data packet 10. In some examples, determining theclock rate correction 354 includes estimating an end position of themobile node 120, the end position a position of the mobile node 120relative to the fixed node 110 at the end of transmitting the datapacket 10. Determining the clock rate correction 354 may also includedetermining a difference between the current position 342 of the mobilenode 120 and the end position of the mobile node 120 and determining theclock rate correction 354 based on the determined difference between thecurrent position 342 of the mobile node 120 and the end position of themobile node 120. In some implementations, determining the clock ratecorrection 354 further includes adjusting a symbol rate of the datapacket 10 based on the determined difference between the currentposition 342 of the mobile node 120 and the end position of the mobilenode 120. For example, the correction controller 336 may determine theclock rate correction using Equation (7). The adjusted symbol rate maybe equivalent to a symbol count of an uncorrected waveform.

At operation 516, the method 500 includes transmitting, by the dataprocessing hardware 312, the data packet 10 to a mobile node 120 at thedetermined reception time 360 using the determined reception frequency362 compensated by the determined clock rate correction 354.

FIG. 6 is schematic view of an example computing device 600 that may beused to implement the systems and methods described in this document.The computing device 600 is intended to represent various forms ofdigital computers, such as laptops, desktops, workstations, personaldigital assistants, servers, blade servers, mainframes, and otherappropriate computers. The components shown here, their connections andrelationships, and their functions, are meant to be exemplary only, andare not meant to limit implementations of the inventions describedand/or claimed in this document.

The computing device 600 includes a processor 610, memory 620, a storagedevice 630, a high-speed interface/controller 640 connecting to thememory 620 and high-speed expansion ports 650, and a low speedinterface/controller 660 connecting to a low speed bus 670 and a storagedevice 630. Each of the components 610, 620, 630, 640, 650, and 660, areinterconnected using various busses, and may be mounted on a commonmotherboard or in other manners as appropriate. The processor 610 canprocess instructions for execution within the computing device 600,including instructions stored in the memory 620 or on the storage device630 to display graphical information for a graphical user interface(GUI) on an external input/output device, such as display 680 coupled tohigh speed interface 640. In other implementations, multiple processorsand/or multiple buses may be used, as appropriate, along with multiplememories and types of memory. Also, multiple computing devices 600 maybe connected, with each device providing portions of the necessaryoperations (e.g., as a server bank, a group of blade servers, or amulti-processor system).

The memory 620 stores information non-transitorily within the computingdevice 600. The memory 620 may be a computer-readable medium, a volatilememory unit(s), or non-volatile memory unit(s). The non-transitorymemory 620 may be physical devices used to store programs (e.g.,sequences of instructions) or data (e.g., program state information) ona temporary or permanent basis for use by the computing device 600.Examples of non-volatile memory include, but are not limited to, flashmemory and read-only memory (ROM)/programmable read-only memory(PROM)/erasable programmable read-only memory (EPROM)/electronicallyerasable programmable read-only memory (EEPROM) (e.g., typically usedfor firmware, such as boot programs). Examples of volatile memoryinclude, but are not limited to, random access memory (RAM), dynamicrandom access memory (DRAM), static random access memory (SRAM), phasechange memory (PCM) as well as disks or tapes.

The storage device 630 is capable of providing mass storage for thecomputing device 600. In some implementations, the storage device 630 isa computer-readable medium. In various different implementations, thestorage device 630 may be a floppy disk device, a hard disk device, anoptical disk device, or a tape device, a flash memory or other similarsolid state memory device, or an array of devices, including devices ina storage area network or other configurations. In additionalimplementations, a computer program product is tangibly embodied in aninformation carrier. The computer program product contains instructionsthat, when executed, perform one or more methods, such as thosedescribed above. The information carrier is a computer- ormachine-readable medium, such as the memory 620, the storage device 630,or memory on processor 610.

The high speed controller 640 manages bandwidth-intensive operations forthe computing device 600, while the low speed controller 660 manageslower bandwidth-intensive operations. Such allocation of duties isexemplary only. In some implementations, the high-speed controller 640is coupled to the memory 620, the display 680 (e.g., through a graphicsprocessor or accelerator), and to the high-speed expansion ports 650,which may accept various expansion cards (not shown). In someimplementations, the low-speed controller 660 is coupled to the storagedevice 630 and a low-speed expansion port 690. The low-speed expansionport 690, which may include various communication ports (e.g., USB,Bluetooth, Ethernet, wireless Ethernet), may be coupled to one or moreinput/output devices, such as a keyboard, a pointing device, a scanner,or a networking device such as a switch or router, e.g., through anetwork adapter.

The computing device 600 may be implemented in a number of differentforms, as shown in the figure. For example, it may be implemented as astandard server 600 a or multiple times in a group of such servers 600a, as a laptop computer 600 b, or as part of a rack server system 600 c.

Various implementations of the systems and techniques described hereincan be realized in digital electronic and/or optical circuitry,integrated circuitry, specially designed ASICs (application specificintegrated circuits), computer hardware, firmware, software, and/orcombinations thereof. These various implementations can includeimplementation in one or more computer programs that are executableand/or interpretable on a programmable system including at least oneprogrammable processor, which may be special or general purpose, coupledto receive data and instructions from, and to transmit data andinstructions to, a storage system, at least one input device, and atleast one output device.

These computer programs (also known as programs, software, softwareapplications or code) include machine instructions for a programmableprocessor, and can be implemented in a high-level procedural and/orobject-oriented programming language, and/or in assembly/machinelanguage. As used herein, the terms “machine-readable medium” and“computer-readable medium” refer to any computer program product,non-transitory computer readable medium, apparatus and/or device (e.g.,magnetic discs, optical disks, memory, Programmable Logic Devices(PLDs)) used to provide machine instructions and/or data to aprogrammable processor, including a machine-readable medium thatreceives machine instructions as a machine-readable signal. The term“machine-readable signal” refers to any signal used to provide machineinstructions and/or data to a programmable processor.

The processes and logic flows described in this specification can beperformed by one or more programmable processors, also referred to asdata processing hardware, executing one or more computer programs toperform functions by operating on input data and generating output. Theprocesses and logic flows can also be performed by special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit). Processors suitable for theexecution of a computer program include, by way of example, both generaland special purpose microprocessors, and any one or more processors ofany kind of digital computer. Generally, a processor will receiveinstructions and data from a read only memory or a random access memoryor both. The essential elements of a computer are a processor forperforming instructions and one or more memory devices for storinginstructions and data. Generally, a computer will also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. However, a computer need nothave such devices. Computer readable media suitable for storing computerprogram instructions and data include all forms of non-volatile memory,media and memory devices, including by way of example semiconductormemory devices, e.g., EPROM, EEPROM, and flash memory devices; magneticdisks, e.g., internal hard disks or removable disks; magneto opticaldisks; and CD ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

A software application (i.e., a software resource) may refer to computersoftware that causes a computing device to perform a task. In someexamples, a software application may be referred to as an “application,”an “app,” or a “program.” Example applications include, but are notlimited to, system diagnostic applications, system managementapplications, system maintenance applications, word processingapplications, spreadsheet applications, messaging applications, mediastreaming applications, social networking applications, and gamingapplications.

To provide for interaction with a user, one or more aspects of thedisclosure can be implemented on a computer having a display device,e.g., a CRT (cathode ray tube), LCD (liquid crystal display) monitor, ortouch screen for displaying information to the user and optionally akeyboard and a pointing device, e.g., a mouse or a trackball, by whichthe user can provide input to the computer. Other kinds of devices canbe used to provide interaction with a user as well; for example,feedback provided to the user can be any form of sensory feedback, e.g.,visual feedback, auditory feedback, or tactile feedback; and input fromthe user can be received in any form, including acoustic, speech, ortactile input. In addition, a computer can interact with a user bysending documents to and receiving documents from a device that is usedby the user; for example, by sending web pages to a web browser on auser's client device in response to requests received from the webbrowser.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the disclosure. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. A method comprising: receiving, at dataprocessing hardware of a mobile node, a current velocity of the mobilenode and a current position of the mobile node relative to a fixed node,the mobile node moving toward or away from the fixed node; identifying,by the data processing hardware, a receive time slot for the fixed nodeto receive a transmission of a data packet from the mobile node;determining, by the data processing hardware, a propagation delay forthe data packet between the mobile node and the fixed node based on thecurrent position of the mobile node relative to the fixed node;determining, by the data processing hardware, a transmission time basedon the identified receive time slot and the determined propagationdelay; determining, by the data processing hardware, a Doppler shiftbased on the current velocity of the mobile node; determining, by thedata processing hardware, a transmission frequency based on thedetermined Doppler shift; determining, by the data processing hardware,a clock rate correction, the clock rate correction accounting for achange in the propagation delay during transmission of the data packet;and transmitting, by the data processing hardware, the data packet tothe fixed node at the determined transmission time using the determinedtransmission frequency compensated by the determined clock ratecorrection.
 2. The method of claim 1, wherein determining thetransmission time comprises subtracting the propagation delay from theidentified receive time slot.
 3. The method of claim 1, whereindetermining the transmission frequency comprises adding the Dopplershift to a base transmission frequency or subtracting the Doppler shiftfrom the base transmission frequency.
 4. The method of claim 1, whereindetermining the clock rate correction comprises: estimating an endposition of the mobile node, the end position a position of the mobilenode relative to the fixed node at an end of transmitting the datapacket; determining a difference between the current position of themobile node and the end position of the mobile node; and determining theclock rate correction based on the determined difference between thecurrent position of the mobile node and the end position of the mobilenode.
 5. The method of claim 4, wherein determining the clock ratecorrection further comprises adjusting a symbol rate of the data packetbased on the determined difference between the current position of themobile node and the end position of the mobile node.
 6. The method ofclaim 5, wherein the adjusted symbol rate is equivalent to a symbolcount of an uncorrected waveform.
 7. A method comprising: receiving, atdata processing hardware of a fixed node, a current velocity of a mobilenode and a current position of the mobile node relative to the fixednode, the mobile node moving toward or away from the fixed node;identifying, by the data processing hardware, a receive time slot forthe mobile node to receive a transmission of a data packet from thefixed node; determining, by the data processing hardware, a propagationdelay for the data packet between the fixed node and the mobile nodebased on the current position of the mobile node relative to the fixednode; determining, by the data processing hardware, a reception timebased on the identified receive time slot and the determined propagationdelay; determining, by the data processing hardware, a Doppler shiftbased on the current velocity of the mobile node; determining, by thedata processing hardware, a reception frequency based on the determinedDoppler shift; determining, by the data processing hardware, a clockrate correction, the clock rate correction accounting for a change inthe propagation delay during transmission of the data packet; andtransmitting, by the data processing hardware, the data packet to themobile node at the determined reception time using the determinedreception frequency compensated by the determined clock rate correction.8. The method of claim 7, wherein determining the reception timecomprises adding the propagation delay to the identified receive timeslot.
 9. The method of claim 7, wherein determining the receptionfrequency comprises adding the Doppler shift to a base receptionfrequency or subtracting the Doppler shift from the base receptionfrequency.
 10. The method of claim 7, wherein determining the clock ratecorrection comprises: estimating an end position of the mobile node, theend position a position of the mobile node relative to the fixed node atan end of transmitting the data packet; determining a difference betweenthe current position of the mobile node and the end position of themobile node; and determining the clock rate correction based on thedetermined difference between the current position of the mobile nodeand the end position of the mobile node.
 11. The method of claim 10,wherein determining the clock rate correction further comprisesadjusting a symbol rate of the data packet based on the determineddifference between the current position of the mobile node and the endposition of the mobile node.
 12. The method of claim 11, wherein theadjusted symbol rate is equivalent to a symbol count of an uncorrectedwaveform.
 13. A system comprising: data processing hardware of a mobilenode; and memory hardware in communication with the data processinghardware, the memory hardware storing instructions that when executed onthe data processing hardware cause the data processing hardware toperform operations comprising: receiving a current velocity of themobile node and a current position of the mobile node relative to afixed node, the mobile node moving toward or away from the fixed node;identifying a receive time slot for the fixed node to receive atransmission of a data packet from the mobile node; determining apropagation delay for the data packet between the mobile node and thefixed node based on the current position of the mobile node relative tothe fixed node; determining a transmission time based on the identifiedreceive time slot and the determined propagation delay; determining aDoppler shift based on the current velocity of the mobile node;determining a transmission frequency based on the determined Dopplershift; determining a clock rate correction, the clock rate correctionaccounting for a change in the propagation delay during transmission ofthe data packet; and transmitting the data packet to the fixed node atthe determined transmission time using the determined transmissionfrequency compensated by the determined clock rate correction.
 14. Thesystem of claim 13, wherein determining the transmission time comprisessubtracting the propagation delay from the identified receive time slot.15. The system of claim 13, wherein determining the transmissionfrequency comprises adding the Doppler shift to a base transmissionfrequency or subtracting the Doppler shift from the base transmissionfrequency.
 16. The system of claim 13, wherein determining the clockrate correction comprises: estimating an end position of the mobilenode, the end position a position of the mobile node relative to thefixed node at an end of transmitting the data packet; determining adifference between the current position of the mobile node and the endposition of the mobile node; and determining the clock rate correctionbased on the determined difference between the current position of themobile node and the end position of the mobile node.
 17. The system ofclaim 16, wherein determining the clock rate correction furthercomprises adjusting a symbol rate of the data packet based on thedetermined difference between the current position of the mobile nodeand the end position of the mobile node.
 18. The system of claim 17,wherein the adjusted symbol rate is equivalent to a symbol count of anuncorrected waveform.
 19. A system comprising: data processing hardwareof a fixed node; and memory hardware in communication with the dataprocessing hardware, the memory hardware storing instructions that whenexecuted on the data processing hardware cause the data processinghardware to perform operations comprising: receiving a current velocityof a mobile node and a current position of the mobile node relative tothe fixed node, the mobile node moving toward or away from the fixednode; identifying a receive time slot for the mobile node to receive atransmission of a data packet from the fixed node; determining apropagation delay for the data packet between the fixed node and themobile node based on the current position of the mobile node relative tothe fixed node; determining a reception time based on the identifiedreceive time slot and the determined propagation delay; determining aDoppler shift based on the current velocity of the mobile node;determining a reception frequency based on the determined Doppler shift;determining a clock rate correction, the clock rate correctionaccounting for a change in the propagation delay during transmission ofthe data packet; and transmitting the data packet to the mobile node atthe determined reception time using the determined reception frequencycompensated by the determined clock rate correction.
 20. The system ofclaim 19, wherein determining the reception time comprises subtractingthe propagation delay from the identified receive time slot.
 21. Thesystem of claim 19, wherein determining the reception frequencycomprises adding the Doppler shift to a base reception frequency orsubtracting the Doppler shift from the base reception frequency.
 22. Thesystem of claim 19, wherein determining the clock rate correctioncomprises: estimating an end position of the mobile node, the endposition a position of the mobile node relative to the fixed node at anend of transmitting the data packet; determining a difference betweenthe current position of the mobile node and the end position of themobile node; and determining the clock rate correction based on thedetermined difference between the current position of the mobile nodeand the end position of the mobile node.
 23. The system of claim 22,wherein determining the clock rate correction further comprisesadjusting a symbol rate of the data packet based on the determineddifference between the current position of the mobile node and the endposition of the mobile node.
 24. The system of claim 23, wherein theadjusted symbol rate is equivalent to a symbol count of an uncorrectedwaveform.